Preparation

Make dipping sauce
In small saucepan over moderate heat, stir together all ingredients. Bring to simmer, then remove from heat and keep warm. (DO AHEAD: Sauce can be made ahead, refrigerated in covered container up to 2 days, and rewarmed over moderate heat before serving.)

Make tempura
Bring medium pot water to boil over high heat. Have large bowl ice water ready. Add green beans to boiling water and blanch just until crisp-tender, about 30 seconds. Using slotted spoon, immediately transfer to ice water to stop cooking, then drain well and dry on paper towels.

Make several shallow cuts across inside curve of each shrimp and gently press shrimp flat on cutting board (to help prevent curling during cooking). Sprinkle shrimp with salt and pepper.

In large saucepan over moderate heat, heat 4 inches of oil until thermometer registers 325°F.

In large mixing bowl, whisk together flour, baking powder, and sesame oil. Gradually and gently whisk in 2 1/2 cups ice water, mixing just until dry ingredients are moistened. (Batter will be very lumpy.)

Working in batches, using tongs or chopsticks dip shrimp and vegetables into batter and fry, turning occasionally, until golden, about 1 1/2 minutes for green beans, 2 minutes for shrimp and other vegetables. Transfer to paper towels to drain. Return oil to 325°F between batches and, using spider or slotted spoon, remove any residual bits of batter from oil before adding next batch.

To fry shiso leaves, gently lay each leaf on top of batter to coat 1 side, then drop, batter-side-down, into oil and fry without turning until underside is golden, about 1 minute. Transfer to paper towels to drain.